Most swash-plate-type refrigerant gas compressors used in today's automobile air conditioning systems syphon refrigerant gas returning from the air conditioning system in a multi-cylinder pump. There, the returning gas is compressed by pistons which are operated by a single rotary swash-plate. After compression, the refrigerant gas is discharged from cylinder bores into discharge chambers and is distributed via a discharge cavity through passageways toward a cooling circuit of the air conditioning system.
During compression and discharge of the refrigerant gas, there is a pulsation in the discharge pressure of the gas imposed by reciprocating motion of the pistons. Among other factors, the frequency of pulsation per pump cycle is a function of the number of cylinder bores. Such pulsation requires suppression if noise and vibration problems are to be abated.
Conventional approaches to such problems have provided a chamber with a substantial volume which acts as a muffling chamber. Such approaches are exemplified in U.S. Pat. No. 4,610,604 which issued on Sept. 9, 1986. The disclosure of that patent is hereby incorporated by reference.
As disclosed therein, after compression, refrigerant gas is choked by restraining orifices before entering a muffling chamber and undergoing rapid expansion. Following such teachings, sudden expansion and subsequent choking of refrigerant gas tends to suppress the pulsation caused by reciprocating motion of the pump's pistons. In such approaches, a relatively large volume of muffling chambers is needed to obtain the desired efficiency and frequency of suppression.
Pulsation phenomena in air conditioning pumps can be thought of as a repetitive rise and fall in localized gas pressure. Individual pulses are generated by the member pistons associated with the air conditioning pump. Such pulsation phenomena can be expressed in wave form which graphically symbolizes the relationship of pressure and time at a given sensing location. An increase in the amplitude of pulsation occurs where individual pressure waves become superimposed and augment each other. To achieve a low level of discharge pulsation, the shape of the resultant discharge wave requires accurate, consistent pulse separation. In prior approaches, small phase shifts in the resultant wave form due to the differing effective travel distances from the cylinder port to the pump discharge port may create superposition of individual waves and substantial increases in pulsation levels.
As noted earlier, existing discharge cavity designs may utilize relatively voluminous muffler cavities near the center of the pump to mix the waveforms from the front and rear cylinder heads in order to offset disadvantages which are inherent in the firing sequence of conventional swash-plate designs. While such muffler cavity designs may tend to reduce the overall pulsation level, they generally fail to compensate for variable phase shift caused by the activation sequence of pistons being displaced by the swash-plate. Additionally, such designs also tend to be more complex and costly than may be necessary in light of the present invention.